adjust option in georeferencing an aerial photo

Hi guys,I am trying to georeference an aerial photograph on the basis of a shapefile layer with contours, roads and houses. I attach the image. Effectively, there is a cloud of points in the middle and lower portion of the image where the residual error is very low (< 3 m). However, there also some further away points (N and E) where the error goes up to 7-8 m. These latter, however, are key points because are the only ones I could find there, so I do not want to lose it just for the sake of reducing the RMS. The question is: shall I apply a 3rd polynomial transformation or the adjust one? How does the adjust transformation really work?Many thanks,Matteo